Winston Peters' refusal to say who he would support after the election has voters almost evenly divided about who he might back to form a government, if he is cast again as the kingmaker.

Asked which party Peters, the NZ First leader, would support to form a government, 32.1 per cent of those surveyed in the latest stuff.co.nz/Ipsos poll expect him to back National, while 29.2 per cent said they expected him to go with Labour.

One in five of those polled said they thought Peters would go with neither Labour nor National, and 18.7 per cent said they did not know.

Twice in the past Peters has been in a position to determine whether National or Labour formed a government.

In 1996 he backed National for a third term under Jim Bolger and in 2005 he backed Labour for a third term under Helen Clark.

Although recent political polls have suggested National could form a government on its own, a single party has never had enough support to rule alone since MMP was introduced in 1996. That means if NZ First gets more than the 5 per cent support required to bring MPs into Parliament without winning an electorate, Peters could again be the kingmaker.

Peters has consistently refused to say who he is likely to support in coalition talks, saying he is opposed to pre-election deals favoured by other parties.

"You don't test the water with both feet," Peters told the Timaru RSA this week, adding that giving hints would weaken his negotiating position.

Although he has primarily targeted National since returning to Parliament following the 2011 election, attacking the Government on its asset sales programme, Peters said Labour was also promoting policies to which NZ First was strongly opposed.

Before the 2011 election, NZ First warned it could not support a Labour government proposing to raise the retirement age and to extend capital gains tax in the way it was proposing. Labour leader David Cunliffe has affirmed both policies going into the September 20 election.

"I think that lost them [Labour] the election [in 2011]," Peters said in an interview this week. "Don't they get it?"

Meanwhile, he hinted this week that he may stand in an electorate this year, something he didn't do in 2011. Although he did not name the seat, the hint was it could be East Coast Bays, where there are persistent rumours that long time local MP Murray McCully could stand aside, with National not fielding a candidate, in a bid to gift the seat to Conservative leader Colin Craig.